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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Qt Tutorial - Chapter 5: Building Blocks</h1>
<p> <center><img src="t5.png" alt="Screenshot of tutorial five"></center>
<p> This example shows how to create and connect together several widgets
by using signals and slots, and how to handle resize events.
<p> <pre>/****************************************************************
**
** Qt tutorial 5
**
****************************************************************/
#include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
#include <<a href="qslider-h.html">qslider.h</a>>
#include <<a href="qlcdnumber-h.html">qlcdnumber.h</a>>
#include <<a href="qfont-h.html">qfont.h</a>>
#include <<a href="qvbox-h.html">qvbox.h</a>>
class MyWidget : public <a href="qvbox.html">QVBox</a>
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
<a name="f553"></a>MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qvbox.html">QVBox</a>( parent, name )
{
<a href="qpushbutton.html">QPushButton</a> *quit = new <a href="qpushbutton.html">QPushButton</a>( "Quit", this, "quit" );
quit-><a href="qwidget.html#setFont">setFont</a>( QFont( "Times", 18, QFont::Bold ) );
<a href="qobject.html#connect">connect</a>( quit, SIGNAL(<a href="qbutton.html#clicked">clicked</a>()), qApp, SLOT(<a href="qapplication.html#quit">quit</a>()) );
<a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
<a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
slider-><a href="qslider.html#setValue">setValue</a>( 0 );
<a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), lcd, SLOT(<a href="qlcdnumber.html#display">display</a>(int)) );
}
int main( int argc, char **argv )
{
<a href="qapplication.html">QApplication</a> a( argc, argv );
MyWidget w;
a.<a href="qapplication.html#setMainWidget">setMainWidget</a>( &w );
w.<a href="qwidget.html#show">show</a>();
return a.<a href="qapplication.html#exec">exec</a>();
}
</pre>
<p> <h2> Line-by-line Walkthrough
</h2>
<a name="1"></a><p> <pre> #include <<a href="qapplication-h.html">qapplication.h</a>>
#include <<a href="qpushbutton-h.html">qpushbutton.h</a>>
#include <<a href="qslider-h.html">qslider.h</a>>
#include <<a href="qlcdnumber-h.html">qlcdnumber.h</a>>
#include <<a href="qfont-h.html">qfont.h</a>>
#include <<a href="qvbox-h.html">qvbox.h</a>>
</pre>
<p> Three new include files are shown here. qslider.h and qlcdnumber.h are there
because we use two new widgets, <a href="qslider.html">QSlider</a> and <a href="qlcdnumber.html">QLCDNumber</a>. qvbox.h is
here because we use Qt's automatic layout support.
<p> <pre> class MyWidget : public <a href="qvbox.html">QVBox</a>
{
public:
MyWidget( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 );
};
</pre>
<p> <a name="constructor"></a>
<pre> MyWidget::MyWidget( <a href="qwidget.html">QWidget</a> *parent, const char *name )
: <a href="qvbox.html">QVBox</a>( parent, name )
{
</pre>
<p> MyWidget is now derived from <a href="qvbox.html">QVBox</a> instead of <a href="qwidget.html">QWidget</a>. That way we use
the layout of the QVBox (which places all of its children vertically
inside itself). Resizes are now handled automatically by the QVBox and
therefore by MyWidget, too.
<p> <pre> <a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" );
</pre>
<p> <tt>lcd</tt> is a QLCDNumber, a widget that displays numbers in an LCD-like
fashion. This instance is set up to display two digits and to be a child of
<em>this</em>. It is named "lcd".
<p> <pre> <a href="qslider.html">QSlider</a> * slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" );
<a name="x2315"></a> slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 );
<a name="x2316"></a> slider-><a href="qslider.html#setValue">setValue</a>( 0 );
</pre>
<p> <a href="qslider.html">QSlider</a> is a classical slider; the user can use the widget to drag
something to adjust an integer value in a range. Here we create a
horizontal one, set its range to 0-99 (inclusive, see the <a href="qrangecontrol.html#setRange">QSlider::setRange</a>() documentation) and its initial value to 0.
<p> <pre> <a name="x2317"></a><a name="x2314"></a> <a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), lcd, SLOT(<a href="qlcdnumber.html#display">display</a>(int)) );
</pre>
<p> Here we use the <a href="signalsandslots.html">signal/slot mechanism</a>
to connect the slider's valueChanged() signal to the LCD number's
display() slot.
<p> Whenever the slider's value changes it broadcasts the new value by
emitting the valueChanged() signal. Because that signal is connected to
the LCD number's display() slot, the slot is called when the signal is
broadcast. Neither of the objects knows about the other. This is
essential in component programming.
<p> Slots are otherwise normal C++ member functions and follow the normal
C++ access rules.
<p> <h2> Behavior
</h2>
<a name="2"></a><p> The LCD number reflects everything you do to the slider, and the
widget handles resizing well. Notice that the LCD number widget
changes in size when the window is resized (because it can), but the
others stay about the same (because otherwise they would look stupid).
<p> (See <a href="tutorial1-01.html#compiling">Compiling</a> for how to create a
makefile and build the application.)
<p> <h2> Exercises
</h2>
<a name="3"></a><p> Try changing the LCD number to add more digits or <a href="qlcdnumber.html#setMode">to change mode.</a> You can even add four push
buttons to set the number base.
<p> You can also change the slider's range.
<p> Perhaps it would have been better to use <a href="qspinbox.html">QSpinBox</a> than a slider?
<p> Try to make the application quit when the LCD number overflows.
<p> You're now ready for <a href="tutorial1-06.html">Chapter 6.</a>
<p> [<a href="tutorial1-04.html">Previous tutorial</a>]
[<a href="tutorial1-06.html">Next tutorial</a>]
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